**Numerical Investigation of Aerodynamic Drag and Pressure Waves in Hyperloop Systems**

### **Thi Thanh Giang Le 1, Kyeong Sik Jang 1, Kwan-Sup Lee 2 and Jaiyoung Ryu 1,3,\***


Received: 7 September 2020; Accepted: 2 November 2020; Published: 6 November 2020

**Abstract:** Hyperloop is a new, alternative, very high-speed mode of transport wherein Hyperloop pods (or capsules) transport cargo and passengers at very high speeds in a near-vacuum tube. Such high-speed operations, however, cause a large aerodynamic drag. This study investigates the effects of pod speed, blockage ratio (BR), tube pressure, and pod length on the drag and drag coefficient of a Hyperloop. To study the compressibility of air when the pod is operating in a tube, the effect of pressure waves in terms of propagation speed and magnitude are investigated based on normal shockwave theories. To represent the pod motion and propagation of pressure waves, unsteady simulation using the moving-mesh method was applied under the sheer stress transport *k* −ω turbulence model. Numerical simulations were performed for different pod speeds from 100 to 350 m/s. The results indicate that the drag coefficient increases with increase in BR, pod speed, and pod length. In the Hyperloop system, the compression wave propagation speed is much higher than the speed of sound and the expansion wave propagation speed that experiences values around the speed of sound.

**Keywords:** Hyperloop system; transonic speed; aerodynamic drag; drag coefficient; pressure wave; shockwave
